Present invention relates to a compressive-type load cell used in load detecting apparatuses for industrial use such as a hopper scale and a tank scale and to a load detecting apparatus provided with the load cell.
FIG. 11A shows an example of a conventional diaphragm type load cell 1 which is attempted to thin.
A circle bore 3 is formed on a lower surface 2a of a short column elastic body 2. A bottom wall of the circle bore 3 constitutes a strain occurrence portion 4. Strain gages 5 are stuck on a lower surface of the strain occurrence portion 4. These strain gages 5 are connected with each other to constitute a well-known Wheatstone bridge (not shown). Numeral 6 denotes a diaphragm which closes the circle bore 3. On the other hand, a load acting portion 7 of short column configuration is projected upwardly from a center portion of an upper surface of the strain occurrence portion 4.
When a compressive load "W" is applied to a load acting surface 7a constituted by an upper end of the load acting portion 7, the strain occurrence portion 4 is deformed according to the value of the compressive load "W".
Deformation quantity of the strain occurrence portion 4 is detected as variation of output level of the Wheatstone bridge circuit comprising the strain gages 5. The value of the compressive load "W" is measured on the basis of the variation.
However, as shown in FIG. 11A, since load transmission paths "p" from the load acting surface 7a to the each strain gage 5 are parabolic curve without turn-back portion, the length of the load transfer path "p" is short. Thus, when an action axis "L.sub.W " is shifted to a center axis "L.sub.C " of the load cell 1, the shift of the action axis "L.sub.W " has large influence to the deformation quantity of the strain acting portion 4, thereby measurement error may occur.
Further, since the load acting portion 7 of the load cell 1 is projected from the center potion of the strain occurrence portion 4, as shown in FIGS. 11B and 11C, when a lateral load "F" which is orthogonal to the compressive load "W" is applied to the load acting portion 7, bending moment "M" (M=F*L: "L" is a distance form load to a neutral axis plan of the strain acting portion 4) is applied to the strain occurrence portion 4. This bending moment "M" may cause measurement error.
As described above, in the conventional load cell 1, there is high possibility to cause measurement error and it is difficult to execute load measuring with high accuracy.